This invention relates to the electromagnetic testing of wire ropes.
Steel hoist ropes are vital components used in many industrial applications and particularly in deep level mining. The ropes are of prime importance from a safety and production point of view and it is therefore necessary that the ropes are examined regularly to ensure that operational standards are consistently being maintained.
Currently, wire ropes are electromagnetically tested to determine variations in three characteristics, namely the cross-sectional area of the rope, wire contact within the rope, and broken wires. Each of these characteristics is hereinafter briefly commented upon.
Cross-sectional area: the strength of a rope is dependent on its cross-sectional steel area which can, for example, be reduced by normal wear and tear, corrosion, and stretch necking of a weak part.
Wire contact: a rope is made up of strands which in turn are made up of individual carbon steel wires wound together in a particular pattern or lay. Each wire makes physical contact with adjacent wires in a particular fashion, the total effect of which is characteristic of the rope in question. If a rope is damaged, for example by having been kinked or bent beyond its elastic limit, the contact pattern of the wires changes. It is important to detect such changes in contact pattern for they may precede a failure of the rope.
Broken wires: a multiplicity of broken wires over a short length of a rope seriously affects the strength of the rope. Broken wires arise from a variety of causes such as, for example, vibration modes which are set up in the ropes during the cycle of acceleration, steady speed and deceleration. It is clearly important to detect broken wires wherever they may be inside a rope.
Historically the cross-sectional area of a rope and the wire contact characteristic have been measured with a device referred to as an AC rope tester. Such a device is disclosed, for example, in the specification of South African Pat. No. 69/6054. The broken wire characteristic on the other hand has been measured with the aid of an instrument referred to as a DC rope tester typified for example in the specification of South African Pat. No. 69/6269. The applicant is also aware of cross-sectional area measurements having been made with a DC rope tester.
Other literature of which the applicant is aware is the specifications of U.K. Pat. Nos. 1231641, 1476773, 1504404, 1531825, and 1565508 and French Pat. No. 2083900.
To the applicant's knowledge the aforementioned rope characteristics have hitherto been measurable only by employing two distinct instruments.
Modern requirements arising from the demands for increased productivity, simplicity, cost effectiveness, and the availability and expertise of skilled non-destructive testing personnel have demonstrated the need for a single instrument which is capable of simultaneously measuring each of the three aforementioned characteristics.